Poly (ethylene terephthalate) fiber (hereinafter referred to as “PET fiber”) is recognized as a most suitable synthetic fiber for use in clothing, and is manufactured world wide in vast amounts by in the fiber industry.
Poly (trimethylene terephthalate) fiber (hereinafter referred to as “PTT fiber”) is known in the prior art literatures such as (A) J. Polymer Science; Polymer Physics Edition Vol. 14 P263–274 (1976), (B) Chemical Fibers International Vol. 45, April (1995) 110–111, (C) Japanese Unexamined Patent Publication (Kokai) No. 52-5320, (D) Japanese Unexamined Patent Publication (Kokai) No. 52-8123, (E) Japanese Unexamined Patent Publication (Kokai) No. 52-8124, (F) WO99/27168 and so on.
The prior art documents (A) and (B) describe some basic properties of PTT fiber such as stress-elongation characteristic and the like, and suggest that the fiber material is suitable for use in clothing in which a low initial modulus property and excellent stretch recovery are required, and in carpets and the like articles.
In Documents (C), (D), (E) and (F), several methods of improving the fiber in thermal dimensional stability and stretch recovery have been proposed for promotion of the best use of the afore-mentioned inherent characteristics of PTT fiber.
As a PTT fiber obtained by high speed spinning, a pre-oriented yarn for drawing is described in Document (G) Japanese Unexamined Patent Publication (Tokuhyo) No. 9-509225 and (H) Japanese Unexamined Patent Publication (Kokai) No. 58-104216, and a partially oriented yarn for use in draw false-twist texturing is disclosed in (I) Chemical Fibers International Vol. 47, February, 1997, pages 72 to 74 and (J) Japanese Unexamined Patent Publication (Kokai) No. 2001-20136. Meanwhile, a preoriented yarn of PTT fiber provided for producing a knitted or woven fabric without drawing (with the elimination of drawing) is proposed in (K) Japanese Examined Patent Publication (Kokoku) No. 63-42007.
A yarn wound at a spinning speed of 2000 to 5000 m/min is described in Document (G), and a preoriented yarn having a birefringence of 0.035 or greater obtained by spinning at a spinning speed of 2000 m/min or more, which is provided for drawing, is described in Document (H). In document (I), a partially oriented yarn for false-twist texturing is described; the partially oriented yarn is a PTT yarn obtained by a spinning process in which the spun yarn is wound at a speed of from 3,000 to 6,000 m/min either not through a godet roll or through a heated godet roll.
According to a study by the inventors, the pre-oriented yarns prepared by the methods described in Documents (G) to (I) are highly oriented, but are scarcely crystallized to have a glass transition temperature ranging from 35 to 45° C. A less or non-crystallized pre-oriented yarn is much move sensitive to a variation in the ambient temperature and moisture. For example, the temperature of a package of a pre-oriented yarn rises during take-up winding step by the transfer of heat generated in the motor on a take-up winder and the heat generated by friction between the package and the pressing roll. When the temperature of the package rises due to such a cause, the preoriented yarn is shrunk on the package during winding.
The shrinkage of a preoriented yarn during winding scarcely occurs at the traverse stroke end portions of the package where the yarn is accumulated to form a hard layer of yarn, and rather occurs mainly around the middle portion of the accumulated layer of the wound yarn. As a result, the package comes to form protruded end portions at its end face corners during take-up winding. Once the protruded high portions are formed, with the increase of amount of wound layer, the generation of frictional heat is concentrated on the protruded high portions of the wound package. As a result, a package wound-up in a prescribed diameter of take-up winding forms a package with two protruding end corners at which the diameter is greater than the diameter of the middle potion of the package; the formation of a package with protruding high end portions. FIG. 1 is a drawing that illustrates schematically the shape of a package with no protruded end portions. FIG. 2 shows schematically another form of package with protruded end portions.
In a package with protruding end portions, the yarn accumulated at the traverse stroke end portions and accumulated at the middle portions differ in thermal characteristic and yarn size.
The preoriented yarn wound at stroke end portions and that wound at the middle portion have different thermal shrinkage stress values (dry thermal shrinking stress), which is measured using a device herein after described. Generally, a thermal shrinking stress value at the stroke end portions of package is greater than that of the preoriented yarn wound at the middle portion of package. When a fabric is formed of the yarn, the difference in thermal shrinkage characteristic contained in the yarn comes to be seen as a difference in shrinking ratio.
Variation of yarn size shows a periodic change corresponding to the length (one traverse stroke) of yarn or two strokes corresponding to the length (one traverse stroke) of yarn from one end of the package to the other end of the package or 2 strokes formed by traversing strokes of the winding machine on which the preoriented yarn is taken up. In FIGS. 3 and 4, examples of yarn size variation charts measured by an evenness tester while a preoriented yarn is being unreeled from the package on which the yarn is wound. FIG. 3 is a chart corresponding to the package shown in FIG. 1, and FIG. 4 is a chart corresponding to the package shown in FIG. 2. In the measurement charts, the periodic variation is observed as hair-like signals equidistantly extending downward towards the smaller yarn size side. The existence of downward signals suggests that the yarn size (=thickness of yarn) at the point in the lengthwise direction of yarn changes towards smaller yarn size.
When a preoriented yarn package in which the defects mentioned above dwell is used either for making fabric, or for draw-false-twist texturing, the resultant products are liable to produce periodical unevenness of dyeing and/or luster, because the package generally is poor in even dyeability. It has been estimated that quality of final fabric goods made from the preoriented yarn package is exceedingly lowered.
In the meantime, Document (K) discloses a process comprising spinning a PET compounded with PTT and/or poly (butylene terephthalate), solidifying the extruded yarn by cooling, heat-treating the solidified yarn by means of a heated roll and subsequently winding at a rate of 3,500 m/min or more. In a comparative example disclosed in the prior art document, a PET homopolymer and a copolymer of PTT composed of PTT homopolymer blended with a PET at 10% by weight is spun at a spinning speed of 4,000 m/min. With the heated-roll at a temperature of 180° C. in the same manner as mentioned above, and the resultant yarn is used without being drawn for making a knitted or a woven fabric.
A study made by the inventors has revealed that a package having a diameter of winding of about 20 to 40 cm, that is economically required, cannot be obtained because the package tends to collapse with an increase in its diameter in a condition where the heat treatment is applied to the yarn during winding at an elevated temperature exceeding 180° C.
The undrawn yarn is frequently broken or fluffed during the heat-treatment at such an elevated temperature because the melting point of PTT is 230° C. Accordingly, the technique of the prior art cannot satisfy commercial-scale production.
The prior art Document (J) discloses a preoriented yarn in which the yarn is heat-treated by means of a godet roll heated at a temperature of from 70 to 170° C. before the yarn is taken up by winding. The method disclosed in the prior art provides a package by which a stabilized draw false-twist texturing of preoriented yarn can be performed for a prolonged period of time. However, it has been found that the method of the prior document does not provide effective means for removing the problems of the protruded edge formation due to the build-up of heat on the package during winding and the periodic occurrences of uneven dyeing caused therefor.
As can be understood from the discussion set forth above, no package enabling production of a fabric, either woven or knitted fabric, in good quality, is known in the prior art relating to a PTT preoriented yarn.
The object of the invention is to provide an improved PTT preoriented yarn package suitable for producing clothing and a process for producing such a package in a stable industrial operation; a preoriented yarn wound on the package is used without drawing, or after being processed into a draw false-twist textured yarn, for either weaving or knitting to produce a fabric having a good quality free from dyeing defects such as a periodically occurring unevenness of dyeing and having softness.
A further specific object of the invention is to provide a PTT preoriented yarn package which is obtained by winding the PTT preoriented yarn and in which the thermal shrinkage variation and yarn size variation of the preoriented yarn, which characteristics are attributable to the edge portion of the package, are removed.
1, polymer tip drying apparatus; 2, extruder; 3, vent; 4, spin-head; 5, spin-pack; 6, spinning nozzle; 7, multifilamentary yarn; 8, cooling air flow; 9, spin oil applicator; 10, heated godet roll; 11, godet roll and 12, preoriented yarn package
FIG. 8 shows the relation between the heat-treating temperature and winding speed in the preparation of a preoriented yarn package according to the invention.